1. Field of the Invention
The present invention relates to an optical pickup apparatus recording information on an optical disc or reproducing information recorded on an optical disc.
2. Description of the Prior Art
Recently, according to rapid development of disc mediums in relation to the optics, various optical pickup apparatus for recording/reproducing information onto/recorded on an optical disc are being developed.
Generally, an optical pickup apparatus includes an optical pickup actuator operating an objective lens in order to make an optical spot of an optical beam of the objective lens follow the center of signal tracks of an optical disc against a surface vibration and an eccentricity, etc. due to rotation of the optical disc.
The optical pickup actuator controls the objective lens so as to perform a focusing operation and a tracking operation.
Herein, the focusing operation means operating the objective lens up and down in order to make an optical spot of an optical beam of the objective lens place within a depth of focus, and the tracking operation means operating the objective lens right and left in order to make an optical spot of an optical beam of the objective lens follow the center of signal tracks of an optical disc.
In more detail, corresponding to an optical pickup, a position of a disc track can be varied relatively by an error and deformation in a manufacture process, a vibration due to rotation of the optical disc and an error of the optical pickup itself, etc., in order to compensate the variation of the position of the disc track an object lens is operated by an optical pickup actuator with electric signals
The optical pickup actuator operates the object lens by an electromagnetic force generating between a current of a coil and a magnet by using the coil and the magnet.
FIG. 1A is a plan view illustrating an optical pickup actuator in accordance with the prior art, and FIG. 1B is a front view illustrating the optical pickup actuator in accordance with the prior art.
The optical pickup actuator in accordance with the prior art includes an objective lens 101 at the center portion, a lens holder 102 having coils 105, 106 on a circumference for tracking and focusing operations, a plurality of magnets 103 and a plurality of yokes 104 separately installed at both sides of the lens holder 102 in order to construct a magnetic circuit, a plurality of suspension wires 107 separately fixed to a plurality of protrusion portions 108 of the lens holder 102 in order to support the lens holder 102, and a damper holder 109 fixed to a base 100 and fixing the other end of each of the plurality of suspension wires 107.
Herein, a focusing coil 105 is wound on the circumference of the lens holder 102 in order to perform the focusing operation, and a tracking coil 106 is wound on each corner portion.
Each of the plurality of yokes 104 made with a ferromagnetic material and projected from the base 100 is placed on the right side or the left side of the lens holder 102, each of the plurality of magnets 103 is fixed inside each yoke 104.
The plurality of protrusion portions 108 are formed at the center portion of the front and the rear surfaces of the lens holder 102, an end of each suspension wire 107 having a two-stage structure is brazed on each protrusion portion 108, the other end of each suspension wire 107 is connected to a PCB 120 through the damper holder 109.
Herein, a damper (not shown) is placed inside the damper holder 109 in order to give an attenuation characteristic to the suspension wires 107 having a stiffness, the PCB 120 is coupled to the rear of damper holder 109, and the other end of each suspension wire 107 is brazed and fixed to the PCB 120.
The plurality of suspension wires 107 support the lens holder 102 so as to be in a lifting state and transmit an operating signal from the PCB 120 to the focusing coil 105, the tracking 106.
The operation of the optical pickup actuator in accordance with the prior art will now be described.
Because the tracking coil 106 is wound on the lens holder 102 in a certain direction, it generates a magnetic flux in a designated direction when a current flows, the magnetic flux generates an attractive force and a repulsive force by the fixed magnets 103 and an electromagnetic force generated between the tracking coil 106 and the magnets 103.
Herein, as depicted in FIG. 1A, a tracking servo for compensating a tracking error is operated by moving the lens holder 102 back and forth by the attractive force and the repulsive force.
And, being different from the tracking coil 105, because the focusing coil 106 is wound in a vertical direction, a magnetic flux of the focusing coil 106 is generated in up and down directions and generates a power in a vertical direction by electric-magnetically working with a magnetic flux of each magnet 103, accordingly the lens holder 102 moves up and down as the focusing direction, and the focusing servo operates in order to compensate it.
In a moving coil method, the focusing coil 105 and the tracking coil 06 are installed at the circumference of the lens holder 102 and move to a tracking and a focusing directions according to the lens holder 102. On the contrary, in a moving magnet method, a magnet is installed at the circumference of a lens holder and moves according to the lens holder. Herein, both methods use a Lorentz power of Fleming""s left-hand rule.
In the meantime, in a high density disc, because data to be recorded by a unit length of a track increases and the number of tracks increases, a control for reading and writing information on a high density disc can not be performed sufficiently in the conventional actuator as depicted in FIG. 1.
In more detail, as depicted in (a) and (b) of FIG. 2, under the circumstances of a width of a track formed at a disc 110 and a distance from a present track to a next track in accordance with the conventional recording density, it is possible to access data sequentially with movement of a pickup and the lens holder 102 of an actuator.
However, as depicted in (c) and (d) of FIG. 2, in a disc 110xe2x80x2 having a high density format, the conventional optical pickup actuator can not access data accurately.
In order to solve above-mentioned problem, as depicted in FIG. 3, if the lens holder 102 of the actuator performs a tilt operation in a tangential direction and a radial direction on the disc 110xe2x80x2 having the high density format, data can be accessed more accurately.
As depicted in FIG. 4, a tilt component has to be compensated in order to get a laser beam reflected through a reflector 111 be incident on a plane of reflection of the optical disc 110 by an objective lens 101.
However, in order to compensate the tilt component by an operation method of the lens holder, the actuator has to perform not only a translational motion in a tracking direction and a focusing direction but also a tilting motion in a radial direction (X axis rotation mode) and a tangential direction (Y axis rotation mode), it is impossible to perform the tilt motion in the conventional actuator.
Although the lens holder can perform the tilting motion by changing the magnetic field structure (depicted in FIG. 1), a degree of freedom of each of the two-stage suspension wires installed at both sides of the lens holder lowers.
For example, when the actuator operates as a pitching mode as depicted in FIG. 5, it has a resonance frequency (f0) of 2xcx9c5 KHz as depicted in FIG. 6, there is a problem to get an operating sensitivity.
In more detail, because a resonance frequency of a pitching mode as a rotation mode in a tangential direction is not less than 2 Khz due to a big spring constant of the suspension wire for performing the tilting motion in the tangential direction, it is impossible to perform the tilting motion in the tangential direction and get the operating sensitivity.
Herein, as depicted in FIG. 7, in an optical pickup actuator, when the suspension wire 107xe2x80x2 having an one-stage structure supports the lens holder 102xe2x80x2 only at one direction, because a tilting angle occurs always in the focusing motion or the tracking motion, although the actuator is capable of performing a tilting control using the servo, excessive loads occur in the optical pickup actuator.
In the meantime, as depicted in FIG. 8, an actuator support structure according to U.S. Pat. No. 4,811,320 (by SANYO ELECTRIC Co., Ltd., Moriguchi, Japan) will now be described.
In the conventional cantilever type support apparatus depicted in FIG. 1, when a thickness of the suspension wire 107 supporting the lens holder 102 increases, a bending characteristic of the suspension wire 107 is deteriorated and an inherence resonance frequency of the suspension wire 107 heightens, when the lens holder 102 performs the tracking motion or the focusing motion, a support point of the lens holder 102 is concentrated on a certain side of the lens holder 102, accordingly a rolling operation of the lens holder 102 is caused.
The above-mentioned rolling operation of the lens holder 102 was not desirable at the time of application of the U.S. Pat. No. 4,811,329, in order to consist a gravity center of the lens holder with an operation center point of the tracking motion or the focusing motion, SANYO ELECTRIC Co., Ltd. has suggested an actuator support structure as depicted in FIG. 8.
As depicted in FIG. 8, in the actuator support structure according to U.S. Pat. No. 4,811,320, four pairs (i.e., there are the total of 8 pairs when the opposite surface is included) of wires 13, 16 fabricated with the same material and having a different length are placed at side surfaces of the lens holder 1, each two pairs are separately placed at the lower portion and the upper portion of both side surfaces of the lens holder 1.
In more detail, in the patent, the total of eight pairs of wires 13, 16, namely each four pairs of wires 13, 16 are separately placed on each of two flat surfaces parallel to each other.
Herein, in the optical pickup actuator, the support structure of the lens holder can be arbitrarily classified into a two sides support structure forming a support member on both sides of a lens holder, an one side support structure forming a support member on one side of a lens holder, and a two-stage support structure forming separately each of two support members on a upper side portion and a lower side portion of a lens holder. In this classification, the conventional support structure depicted in FIG. 1 is an one side support structure and a two-stage support structure, and the support structure according to U.S. Pat. No. 4,811,320 is a two sides support structure and a two-stage support structure.
Meanwhile, in a two sides two-stage support structure suggested in U.S. Pat. No. 4,811,320, a tilting operation can not be performed, however a tilting operation can be performed in a two sides one-stage support structure in accordance with the present invention.
Because a two sides two-stage support structure according to U.S. Pat. No. 4,811,320 has been suggested in order to restrain unnecessary tilting operation of a lens holder at an extension of an one side two-stage support structure performing the conventional focusing and tracking operations, it is difficult to perform a tilting operation in an optical pickup actuator adopting the two sides two-stage support structure according to U.S. Pat. No. 4,811,320.
In order to solve above-mentioned problem, it is an object of the present invention to provide an optical pickup actuator performable a tilting operation which is capable of accessing data recorded on a high density disc more accurately by performing not only a translational motion in a tracking direction and a focusing direction but also a tilting motion in a radial direction and a tangential direction by installing a plurality of one-stage suspension support means on both sides of a lens holder so as to have an elasticity in order to minimize a constraining force about the lens holder.
In order to achieve above-mentioned object, there is provided an optical pickup actuator performable a tilting operation including two damper holders separately fixed to both sides of a base, a lens holder placed between the damper holders and having an object lens in order to read and write information of an optical disc, two suspension support means separately connected to the damper holder at both sides of the lens holder so as to support the lens holder as a two sides one-stage support structure, and two magnetic operating means separately installed at the lens holder and the base and operating the lens holder so as to follow an optical disc.
Two of the suspension support means are placed on a flat surface so as to be parallel each other.
In an embodiment of the present invention, the suspension support means is constructed with four suspension wires separately connected from the rear and the front of the lens holder to each of both damper holders.
A flexible PCB is placed at the outside of the damper holder in order to an operating signal to the magnetic operating means, its center portion is fixed to the damper holder so as to have a certain distance from the damper holder in order to transmit an operation signal to the magnetic operating means, and the suspension support means are connected to the front and the rear of the flexible PCB by passing through the damper holder so as to be supplied an elasticity.
In another embodiment of the present invention, the suspension support means are constructed with four suspension wires separately connected from both sides of the front and the rear of the lens holder to both damper holders.
In still another embodiment of the present invention, one end of each of the suspension support means is fixed to the one damper holder and the other end of each of the suspension support means is supported by the other damper holder so as to be movable in a length direction.
In yet another embodiment of the present invention, each of the suspension support means has an elastic portion in order to generate an elasticity by varying a length of the elastic portion.
Each suspension support means is constructed with a plate spring, and the elastic portion has a xe2x80x98Sxe2x80x99 shape.